1. Field
The present inventive concept relates to an amplifier, and more particularly, to a half-bridge pulse-width modulation (PWM) amplifier.
2. Description of the Related Art
PWM is a technique of changing a pulse width according to an amplitude of an input signal. PWM has advantages of high efficiency, high resolution, and low power consumption. Thus, PWM is used for amplifiers, for example, class-D amplifiers, and audio systems. Accordingly, a PWM amplifier is called a class-D amplifier. An audio system using PWM usually embeds an audio signal in a PWM signal having a higher frequency compared to a sample rate of the audio signal, when transmitting the audio signal. A PWM amplifier converts an audio signal into a digital PWM signal, amplifies the PWM signal, and outputs it to a speaker or a headphone, for example, a headset or an earphone.
To drive speakers, a full-bridge PWM amplifier is conventionally used. To drive devices like headphones to which an input signal is applied on the basis of zero voltage or a ground level, a half-bridge PWM amplifier is conventionally used. Since a PWM signal is conventionally a two-level signal, a predetermined positive (+) voltage and the ground level or a positive voltage and a negative voltage are switched according to the PWM signal in a two-level PWM driving method.
In the two-level PWM driving method, even when an input signal is “0”, an output terminal still maintains a PWM duty of 50:50 and performs switching. As a result, in addition to dynamic current consumed by an audio signal, static current is always consumed unnecessarily, thereby decreasing output efficiency.